It has been recognized that thiazide diuretics reduce urinary calcium excretion. Additionally, there is information to suggest that the bone mineral density of patients on chronic thiazide therapy is increased. In this project, we employ the technique of dual stable calcium isotope loading to examine the kinetics of bone and urinary calcium flux before and during thiazide administration. Our hypothesis is that this drug directly promotes bone mineral accretion, and that the reduced calcium excretion is a secondary phenomenon.